I have had the chance to test and shoot D3 and D300 today at a Nikon Pro Services day. Both are nice cameras.

I had the chance to play with the high ISO - I also have checked the preformance of low ISO (as both cameras have a base ISO of 200 - with low 1 and low 2 below that). And I have shot some test shots for corner sharpness with 14-24mm and my 17-35mm on the FX camera.
I was able to do test shots both inside and out. While it was not a thorough review (and the cameras were still in pre-release spec) I was able to investigate several of the features that I was particularly interested in.
The D3 also seemed particularly water resistant:

Alex